1. Field of the Invention
This invention relates generally to communication systems, and, more particularly, to wireless communication systems.
2. Description of the Related Art
Conventional wireless communication systems provide wireless connectivity using radio access networks or other wireless entities such as access points, base stations, base station routers, and the like. For example, a mobile unit may establish a wireless communication link over an air interface with a radio access network that is a communicatively coupled to a network. The mobile unit may use the wireless communication link to access services provided by the network such as establishing a communication session with another mobile unit. The information transmitted using the communication session between the two mobile units may be analog or digital information and the communication path between the mobile units may be formed using a circuit-switched architecture or a packet-switched architecture. In a circuit-switched architecture, a dedicated communication path is formed between, for instance, two mobile units and may only be used by the two mobile units. In contrast, packet-switched architectures divide the information up into packets that can be transmitted along numerous paths between the two mobile units using a common packet network infrastructure for forwarding the packets between the mobile units and their network peers. Thus, some or all of the paths through a packet-switched network infrastructure may be shared by other mobile units or other entities coupled to the packet-switched network such as a network server or a fixed subscriber. Moreover, almost all packet-switched wireless systems rely on the Internet Protocol (IP) for routing and forwarding. Packet switched networks are more open and hence vulnerable to attacks. Security is therefore of primary importance in packet-switched networks.
A wireless communication system can be conceptually structured into a multiple layer model. For example, the Open Systems Interconnection (OSI) Reference Model includes seven layers: the application layer, the presentation layer, the session layer, the transport layer, the network layer, the data link layer, and the physical layer. The application layer is the “highest” layer and so it is closest to the end user. The application layer includes software for providing various applications. The presentation layer establishes a context and translates between different application layer entities. The session layer controls sessions established between different computers and manages connections between local and remote applications. The transport layer provides transparent data transfer between end-users and supports reliable data transfer services to upper layers. The network layer provides the functional and procedural support for transferring variable length data sequences from a source to the destination via one or more networks. The data link layer provides the functional and procedural support for transferring data between network entities, as well as providing error correction. The physical layer is the “lowest” layer, which defines the electrical and physical specifications, as well as encoding and modulation schemes needed for error-free transmission between devices.
Numerous wireless access technologies may be implemented at the physical layer and link layer to support packet data applications. Some exemplary wireless access technologies include second generation (2G), third generation (3G), and fourth generation (4G) technologies such as HRPD, 1×-EVDO, UMTS/HSPA, WIMAX/IEEE-802.16, 3GPP2-UMB, and 3GPP-LTE. These wireless access technologies operate according to standards and/or protocols such as the standards and/or protocols established by the Third Generation Partnership Projects (3GPP, 3GPP2) and WiMAX Forum Network Working Group (NWG). To take advantage of the different signal strengths and existing coverage areas of the already deployed technologies, equipment vendors are developing and deploying dual mode (or multi-mode) mobile units that are capable of communicating using multiple wireless access technologies. For example, a dual-mode mobile unit may implement two independent means of IP connectivity that operate according to two different wireless access technologies. At the same time, service providers are increasingly using more than one wireless access technology to provide wireless connectivity. For example, some service providers have deployed heterogeneous networks that include overlaid meshes and/or overlapping coverage areas with different access technologies. The overlaid meshes and overlapping coverage areas may be used as part of an evolution from a legacy technology to a newer technology or for other reasons, such as reducing deployment and/or operating costs, improving the overall communication spectrum characteristics, and the like.
Application layer technologies are also evolving rapidly. For example, new browser technologies are fast replacing older WAP based methods and almost every Internet application is on the cusp of being ‘mobilized’ to cater to mobile subscribers. More Internet Protocol (IP) based mobile-to-mobile services are also being introduced to compliment and upgrade existing cellular mobile-to-mobile services. Examples of these mobile to mobile services include Mobile VoIP complimenting existing cellular voice services, and Mobile IM with text, audio, and video sharing exploring richer versions of conventional cellular SMS. Voice over Internet Protocol (VoIP) is a technique for encoding audio signals (such as voice signals) into a digital format that can be used to form packets for transmission over a packet-switched network which uses the Internet Protocol (IP) at the network layer. The VoIP packets are typically referred to as delay-intolerant and jitter sensitive information because large delays in transmission from transmitter to receiver or between successive packets at the destination VoIP session peer (e.g., mobile unit) may degrade the quality of the audio signal produced by the source peer. Consequently, VoIP applications are typically constrained to provide VoIP packets at a selected quality-of-service (QoS) level. For example, a VoIP application implemented in a mobile unit may be required to maintain minimum levels of delay, delay jitter, and the like for packets transmitted over the network. In some cases, customers may pay larger fees to obtain overall higher QoS levels of higher QoS levels for certain applications.
A typical wireless access network is conventionally divided into two components: the radio network and the core network. The conventional core network includes two levels of IP gateways that allow mobile units to access the Internet, as illustrated by the communication network 100 shown in FIG. 1. Visited gateways (VGW) provide an interface between the core network and the radio network, which includes entities such as base stations, base station controllers, base station routers, access points, and the like. Home gateways (HGW) communicate with the visited gateways and provide an interface between the core network and the Internet. The home gateway is typically responsible for IP address assignment and management in addition to serving as the gateway to the Internet. The home gateway and the visited gateway may be separated by one or more peering networks, particularly when the home gateway and the visited gateway are operated by different service providers and/or when the two gateways are geographically or topologically distant from each other, as illustrated by the communication network 200 shown in FIG. 2.
The home gateway, the visited gateway, and any peering networks between these gateways can become choke points for packets traveling to or from the Internet. For example, if two mobile units have an established call session, the core network gateways for the two mobile units may be in two different cities. The base stations that provide the air interfaces may also be in completely different cities than any of the core network gateways. In some cases, the route between a base station and a home gateway may traverse through multiple peering networks in different cities due to peering relationships across backbone operators. Depending on the topology of the network, even calls that are served by the same visited gateway may be routed through numerous gateways and/or peering networks. For example, a call between two users (one from New York City and one from Los Angeles) who are attending a conference in Chicago may have to be routed from Chicago to New York City to Los Angeles and then back to Chicago even though the users may be in the same building when the call is placed. This scenario is sometimes referred to as the “triangle routing problem” because packets are routed from an Internet host through a home agent to a mobile node (i.e., along two legs of a triangle) despite the presence of a direct path from the Internet host to the mobile node (i.e., the hypotenuse of the triangle).
The diversity of real communication networks significantly complicates the triangle routing problem. Due to the geographic diversity in the locations of the user, the radio network, the visited gateway of the core network, and transport within the core network, operators are forced to use various peering points to route traffic to the Internet. In effect, multiple clusters of networks are created with routing and forwarding paths dictated by various standards and peering policies, which can introduce inefficiencies. For example, forced routing of the mobile unit calls through multiple peering points may result in a dramatic increase in end-to-end latency that translates to end-user dissatisfaction, as well as increased cost in transport that may lead to added operating expense (OPEX). The choke points also have the potential to create inefficiencies and large scale outages due to an inherent lack of fault-tolerance. These drawbacks may undermine the efficiency of access to the network provided by evolution in the physical layer and application layer technologies. These effects may also be exaggerated by the fact that a significant percentage of mobile-to-mobile calling may be limited to within a geographic region potentially served by the same visited gateway.
Various Internet-wireless standards drafts and research publications have suggested approaches to ameliorate the triangle routing problem. One technique is a client-based route optimization technique that was adopted as a part of Mobile IPv6. However, this technique requires involvement of the client (e.g., the Internet host and/or the mobile node) and is performed once for each correspondent node. Furthermore, the protocol only applies when both the mobile node and the correspondent node are compliant with IPv6 and can be addressed using IPv6 home and care-of addresses. The client-based route optimization techniques have not been widely implemented because they are elaborate, cumbersome, and prone to security lapses.
Another approach to addressing the triangle routing problem is a policy based local breakout technique that uses multiple IP addresses for the client and routes specific flows based on policies. The policy-based local breakout techniques are primarily intended to address subscribers that roam from one network to another and/or between multiple service providers. As an example, consider an Asian subscriber visiting a US network. In this case, the policy-based local breakout technique would assign the subscriber to two ‘home’ gateways—one in Asia and the other in the US. One or more policies may then be used to determine how calls are routed. For example, the policies may dictate that latency sensitive calls are routed locally using an IP address assigned by the US home gateway. The policies may further dictate that other applications are routed only through the home gateway in Asia (e.g., a music service in the subscriber's language). Applications that are routed through the Asian home gateway will address the user's mobile using the IP address assigned by the Asian home gateway.
Another alternative is to utilize media-aware routing concepts that can be used in heterogeneous networks that communicate with various types of devices (both wired and wireless). For example, a system that implements media-aware routing may attempt to provide an optimal route based on the type of media that is being transmitted. For example, VoIP calls may be routed according to one policy, streaming video may be routed according to another policy, and text messages may be routed according to yet another policy.